In the natural gas industry, recovered natural gas from a production well generally contains a large amount of water mixed in with the gas, which can create problems during recovery and processing of the gas. Specifically, the water may freeze in pipelines and equipment, and/or form hydrates with carbon dioxide and hydrocarbons, which may result in plugging equipment and pipelines. The water often contains acid gas such as hydrogen sulfide (H2S) and carbon dioxide (CO2), that may liquefy and drop out as the temperature or pressure of the gas decreases, thereby causing corrosion in equipment and pipelines. To prevent the aforementioned problems, natural gas is typically dehydrated to remove the water prior to the gas being introduced into pipelines. Triethylene glycol, commonly referred to as glycol, is generally used to dehydrate natural gas.
FIG. 1 illustrates a typical glycol dehydration unit 10 used in the prior art, where lean “dry” glycol 11 under high pressure is fed into a contactor or absorber column 12 where it contacts a “wet” natural gas stream 13 containing water. The dry glycol strips the water from the natural gas 13 by physical absorption in the absorber column and the now dry natural gas 15 exits the top of the absorber column and is fed into a pipeline 17. The wet glycol 19, now containing water and referred to as “rich glycol”, exits the bottom of the absorber column 12 and is fed into a glycol regeneration system.
In a typical glycol regeneration system, the wet glycol 19 first enters a flash tank 21 to remove any hydrocarbon vapors (flash gas 21a) and liquids (skim oil 21b) and to reduce the pressure. Next, the wet glycol 19 is heated in a heat exchanger 16 and fed into a stripper or glycol regenerator 14. The glycol regenerator typically consists of a column 14a, an overhead condenser 14b and a reboiler 14c wherein the glycol is thermally regenerated to remove excess water (water vapor 19a) and leave hot dry glycol 11a. The hot dry glycol is cooled in the heat exchanger 16 to form cool dry glycol 11, which is pumped via a glycol pump 18 through a pressurizing system 23 to increase the glycol pressure to that of the glycol absorber 12 before being fed back into the absorber for re-use.
As is known, glycol may also be used to dehydrate other gases besides natural gas, including CO2, H2S and other oxygenated gases.
One particular problem associated with glycol dehydration processes is the requirement to dehydrate natural gas at locations where grid power is not available. Often Kimray™ “energy exchange pumps” are used to pump glycol through the dehydration system and to pressurize dry glycol to the pressure of the absorber prior to introduction into the absorber. A Kimray™ pump uses high pressure gas from the reservoir to drive a piston motor to pressurize the dry glycol. However Kimray™ pumps rely on high pressures to drive the pump, and thus they often stall or run erratically when there is reduced reservoir pressure, such as 200 psig or lower. Reduced reservoir pressure may be encountered due to normal fluctuations in reservoir pressure during drilling operations, or due to a reservoir having an overall low pressure.
As a result, there is a need for an efficient and effective glycol pump that can be used to dehydrate natural gas from reservoirs having low pressure or variable pressure. There is also a need for a glycol pump that can operate in locations where grid power is not necessarily available. There is a further need for such a pump that produces limited or no greenhouse gas emissions.